Method and apparatus for controlling heat effect in metal cutting operations

ABSTRACT

In a metal cutting apparatus of the type which cuts the metal workpiece by directing a jet of cutting gas against a pre-heated portion of the workpiece, a combination of a cutting tip and a hollow conical coolant nozzle which discharges a swirling sheet of coolant is used to control the distortion and localized hardening of the work caused by the heat effect of the cutting operation.

United States Patent Van Horn Apr. 29, 1975 METHOD AND APPARATUS FOR[56] References Cited CONTROLLING HEAT EFFECT lN METAL UNITED STATESPATENTS CUTTING OPERATIONS 3 ()47 2t)8 7/1962 Cotlnda 239/010, 7 [75]Inventor: Charles A. Van Horn. Country Club 3.319.692 5/1967 Reba ct al239/DIG. 7 Hills [IL 3.758.258 9/1973 Kolhi 239/424 [73] Assignee:Chemetron Corporation, Chicago. i L King Attorney, Agent, or FirmN. M.Esser 22] Filed: Nov. 14, 1973 [21] Appl. No.: 415.838 [57] ABSTRACT uIn a metal cutting apparatus of the type which cuts the Related ApphumonData metal workpiece by directing a jet of cutting gas DlYlSlOIl Of SCI.NO. 2i L217. D60 23. l97l Pill. NO. against a p g-heated portion of thcworkpiece "1 on 33151483- bination of a cutting tip and a hollow conicalcoolant nozzle which discharges a swirling sheet of coolant is Cl239/1325; 239/DIG 71 266/23 P used to control the distortion andlocalized hardening [51] 'l Cl Bosh 15/00 of the work caused by the heateffect of the cutting [58] Field of Search 239/DIG. 7 424, 132.3;Operation 5 Claims. 5 Drawing Figures l l" l I I I I! I N," s

II I! ll i l l i \i l METHOD AND APPARATUS FOR CONTROLLING HEAT EFFECTIN METAL CUTTING OPERATIONS This is a division of application Ser. No.21 1,217 filed Dec. 23, 1971, now US. Pat. No. 3,815,883.

This invention relates to apparatus for and a method of cooling a metalworkpiece being cut by a jet of gas directed against a pre-heatedportion of the workpiece. The invention relates particularly to acombination of a coolant nozzle and a cutting tip adapted to pre-heatthe metal workpiece and direct a jet of gas against the heated portionof the workpiece, and to a method employing this combination.

Cooling of the cut metal by means of the combination of this inventionminimizes distortion of the metal workpiece which is caused ordinarilyby the temperature difference between the metal near the cut and themore remote portions of the metal workpiece. A particular advantage ofthis invention lies in the superior degree of uniformity of hardness ofthe metal workpiece after being cut as compared to former methods ofcooling the cut metal.

Known methods for cooling, and thereby controlling the distortion of ametal workpiece during a cutting operation, e.g. flame cutting, havelacked the capacity to cool the heavier plate thickness now being cut byhigh speed cutting machines. The method described in US. Pat. No.2,208,121 employs an annular spray conduit which surrounds the cuttingtip of the flame cutting apparatus. The spray conduit is perforatedalong the annular edge facing the workpiece. A coolant such as water isexpressed through the perforations to direct a spray of the coolantagainst the workpiece. The spray consists of discrete streams of coolantwhich, for the most part, break up into droplets as they travel towardthe workpiece. The coolant rebounds from the surface of the workpieceupon striking it and then settles as im mobile pools. In the case ofwater, which is the usual coolant, the formation of a heat-insulatinglayer of steam under the immobile pools prevents the full utilization ofthe coolants capacity to absorb heat.

The hardness of the cut edge of the metal workpiece when cooled by themethod and the apparatus of this invention is demonstrably closer to thehardness of the remainder of the workpiece than that resulting from thecooling method employing a spray of coolant.

Other advantages gained by the use of the inventive method and apparatusincludemore effective entrapment of particulate matter ejected by thecutting gas than heretofore practicable and a lessened formation ofadhesive slag.

One object of this invention, therefore, is to control or minimize thedistortion of a metal workpiece as it is being cut by the impingement ofa high velocity jet of gas against the heated surface of the workpiece.Another object is the minimization of hardness variations between heatedand unheated portions of the metal workpiece. Still another object isthe suppression of the clouds of metallic fines normally produced duringthe cutting operation. A further object is the lessened formation ofadhesive slag. Another important object of the invention is theprovision of a simple, rugged, convenient and easily maintained devicefor use as a cooling adjunct in a cutting apparatus.

In accordance with these objects, a method of cutting a metal workpiecehas been discovered which comprises the steps of heating a portion ofthe metal workpiece to the red heat temperature of the metal, impinginga jet of cutting gas, usually an oxidizing gas such as high purityoxygen, against the pre-heated portion of the workpiece, generating aswirling annular sheet of coolant and directing said sheet of coolantonto the metal workpiece surrounding the point of impingement of the jetof gas. The sheet of coolant spreads outwardly over the surface of theworkpiece as an intact film thereby controlling the heat effect of thecutting opera tion on the workpiece. The sheet of coolant differs from aspray in that a sheet has a continuous and intact surface whereas aspray is composed of droplets.

The heat effect includes distortion of the metal workpiece and hardnessvariations between the heated and unheated portions of the workpiece.The heat effect is particularly significant in the flame cutting offerrous metals and the method of this invention is therefore especiallyuseful in the flame cutting of such metals. Flame cutting commonlyemploys an oxy-acetylene or other oxy-fuel gas torch having a cuttingtip which preheats the metal workpiece to an appropriate temperature anddirects a jet of oxygen against the pre-heated metal to burn away themetal along the lines of impingement of the oxygen. The method may alsobe used in cutting operations wherein a jet of gas such as air, helium,nitrogen, argon and the like is used to cut molten metal from theworkpiece by displacement. The aircarbon arc cutting of metals is anexample. The invention will be described hereinafter with reference toflame cutting but it will be realized that it can be readily adapted torelated types of cutting.

The annular sheet of coolant is generated by a hollo conical nozzlemounted about the cutting tip of a flame cutting torch. A swirlingaction is imparted to the coolant by the shape of the nozzle, causing asheet of coolant to emerge from the nozzle and impinge on the metalworkpiece and spread outwardly over the workpiece as an intact film. Themobility of the intact film effects a vast improvement in the transferof heat from the workpiece to the coolant as compared to the staticpools of coolant which collect during the spraying of discrete amountsof coolant onto the workpiece.

The invention will be better understood by reference to the accompanyingdrawing which illustrates a combination of a hollow conical coolantnozzle and a conventional flame cutting tip which may be used inpracticing the inventive method.

FIG. 1 is an elevational view, partly in section, of the combinationsupported above a metal workpiece, depicting the action of a sheet orfilm of coolant having a continuous surface as it moves from a hollowconical nozzle toward the workpiece and spreads over it as an intactfilm. For clarity of illustration the coolant is not shown within thenozzle.

FIG. 2 is a sectional view of the combination taken along the line 22 ofFIG. 1..

FIG. 3 is a plan view of a nozzle insert used in an alternate embodimentof the hollow conical nozzle shown in FIGS. 1 and 2.

FIG. 4 is a sectional view taken along the line 44 of FIG. 3.

FIG. 5 is a sectional view similar to that of FIG. 4 illustrating anozzle insert used in another embodiment of the hollow conical nozzleshown in FIGS. 1 and 2.

In the combination shown in FIGS. 1 and 2, a hollow conical coolantnozzle 10 is mounted about a flame cutting tip 11 by means of aset-screw 12 or other mounting means. An annular nozzle body 13 isthreaded to receive the set-screw 12. An annulus 14 in nozzle body 13communicates with a coolant conduit 15 through an inlet port 16. Conduit15 is connected to a source (not shown) of a liquid coolant, suchaswater, under pressure. A nozzle insert 17 is removably connected tonozzle body 13 by engagement of threads properly disposed in each. Aperipheral groove 18 in nozzle insert 17 cooperates with annulus 14 innozzle body 13 to form a plenum chamber 19. Alternatively, plenumchamber 19 may be formed by a recess in either the body or insert incooperation with the wall of the other. Slots 20, preferably havingwalls 0.020 inch wide and 0.020 inch deep, are formed transversely inand cross upper annular surface 21 of insert 17 so that coolant passagesbetween plenum chamber 19 and the interior insert 17 are formed incooperation with the upper internal wall of nozzle body 13 adjacentthereto.

The contours of the interior surface 22 of insert 17 are such that itshapes and directs the stream of coolant flowing over it.

Interior surface 22 of insert 17 slopes inwardly at an angle of about 45from upper annular surface 21 to form a vortex generating slopingsurface 23 preferably about one-eighth inch wide. Annular cavity 24through which the coolant swirls, is defined by nozzle throat wall 25and skirt 26 and the external wall of cutting tip 11. Wall 25 defines acylindrical section preferably about one-eighth inch in length and aboutfive-eighths inch in diameter. Skirt 26 tapers away from the axis of thenozzle and defines a frustoconical section having a base preferablyabout 29/32 inch in diameter and about five-eighths inch in length. Theradius of curvature between nozzle throat wall 25 and skirt 26 ispreferably about 0.060 inch. Skirt 26 terminates in an annular step 27at its free end. The nozzle insert 17 at its outer surface is beveled at28 providing a clean breakaway line for the sheet of coolant formed onsurface 22.

In FIG. 2 slots 20 are substantially tangential to the vortex generatingsurface 23. A swirling action is thereby imparted to the coolant flowingonto vortex generating surface 23 from slots 20.

In FIG. 3 an alternate arrangement of eight slots 20 is illustrated. Thethickness of the coolant sheet becomes more uniform as the number ofslots 20 is increased.

In FIG. 4 vortex generating surface 23a slopes at an angle of about 46from upper annular surface 21 toward skirt 26a. Cavity 24a is bounded byskirt 26a and is a frustoconical section. The radius of curvaturebetween vortex generating surface 23a and skirt 26a is about 0.030 inch.

In FIG. vortex generating surface 23b slopes at an angle of about 33from upper surface 21 toward nozzle throat wall 25. The radius ofcurvature between throat wall 25 and skirt 26b is about 0.060 inch.

The angle of inclusion of a frustoconical section is illustrated in FIG.5 as angle 0. This angle may be from about to about 135 but angles fromabout 40 to about 120 are preferable. In FIG. I, 0 is illustrated to beabout 25; in FIG. 4 about 70; and in FIG. 5 about An even number ofslots is illustrated in the drawing. However, it is only necessary thatthere be at least one coolant passage between plenum chamber 19 and theinterior of nozzle 10. There may be from one to about ten slots 20 inupper annular surface 21 or as many as are practicable.

Alternatively, a hollow conical nozzle having a inlet port adapted todirect a stream of coolant approximately tangentially onto a vortexgenerating surface may also be used in lieu of a nozzle having slots forcoolant passages.

The walls of slots 20 form in transverse section three sides of asquare, the fourth side being provided by the upper internal wall ofnozzle body 13. The slots may also be of a rectangular, triangular orother suitable shape. Although 0.020 inch square is an adequatecross-sectional dimension of the slots, it is evident that thedimensions may be larger or smaller depending on other variables such asthe number of slots, the coolant pressure and the diameter of the nozzlethroat (the narrowest cross-section within sleeve member 17, 17a or17b), each of which affects the coolant velocity within the nozzle.

The annular cavity 24 provides sufficient clearance for the flow of thecoolant through the nozzle.

The breakaway line of coolant nozzle 10 may be flush with the distal endof cutting tip 1 l or as much as about 1 inch above it. The distancefrom the workpiece to the nozzle may be from about 0.25 inch to about 2inches or more but fromabout 1 inch to about 2 inches is preferred. Theswirling action of the coolant sheet is maintained over the interveningdistance.

The annular sheet or film of coolant envelops an area on the workpieceof from about 1 inch to about 4 inches or more in diameter. The coolantdoes not appear to interfere with the preheating flame or the jet ofoxidizing cutting gas with the operation of the flame cutting apparatus.7

In operation of the combination of a hollow conical coolant nozzle 10and a cutting tip 11, nozzle 10 in which angle 6 of nozzle insert 17 isabout 49, is mounted on cutting tip 11 which, in turn, is mounted on aflame cutting machine. A coolant such as water is made to flow underpressure through conduit 15 and inlet port 16 into plenum chamber 19 andthen through slots 20 onto vortex generating surface 23. A swirlingaction is imparted to the coolant stream as it impinges on surface 23.The swirling water moves into annular cavity 24 and is formed into asheet or film adhering closely to nozzle throat wall 25. The swirlingsheet follows the contour of the curved surface between wall 25 andskirt 26, assuming a hollow frustum shape as it follows the latter. Thesignificance of step 27 is not fully understood but it appears to causethe sheet of coolant to fan out into an inverted tulip-like shape as ittravels toward the workpiece being cut. The integrity of the sheet orfilm of coolant is maintained as it strikes the metal workpiece andflows across the workpiece absorbing heat from the metal surrounding thepoint of cutting.

The action of hollow conical coolant nozzle 10 is believed to be basedon the well known Coanda effect which includes the phenomenon of a sheetlike stream or film of fluid (gaseous or liquid) attaching itself to asurface and following its contour even about rather sharp curves. Anextreme instance of the Coanda effect is the bending of a stream of airaround a l arc (Scientific American, Vol. 214. pages 8492; June, 1966).One of the factors affecting the tendency of a fluid to adhere to thesurface over which it is flowing is the radius of curvature of thesurface. The radius of curvature of the contour between skirt 26 or 26band throat wall 25 in nozzle insert 17 or 17b and between skirt 26a andvortex generating surface 23a in nozzle insert 17a is sufficient for theCoanda effect to be maintained.

The velocity of the coolant is another factor important to the operationof the Coanda effect. As noted above, the velocity is a function of thecoolant pressure. A minimum pressure of 20 psi is necessary to maintainthe sheet or film of coolant from nozzle insert 17. The maximum rate ofdischarge of water from nozzle insert 17 is about 0.5 gallon per minute.The water attains a velocity of about 6,000 feet per minute as it flowsthrough slots 20 in nozzle insert 17 and onto vortex generating surface23 at the maximum discharge rate.

It will be appreciated that other liquid coolants com monly used forcontrolling the heat effect during metal cutting may be used as well aswater. The embodiments of the invention illustrated and described hereinare merely illustrative and variations which may differ in detail butnot in substance will readily suggest themselves to those skilled in theart.

What is claimed is:

l. A coolant discharging nozzle comprising an annular body having aliquid inlet port, an annular plenum chamber communicating with saidport, a vortex generating surface adapted to receive a liquid flowingfrom said plenum chamber through at least one passage between the plenumchamber and the interior of the nozzle and a contoured surfacecontinuous with said vortex generaating surface, said contoured surfacehaving a portion which tapers away from the axis of the nozzle to formthe boundary of a hollow frustrum having its base at the outlet of thenozzle for shaping and directing a swirling annular sheet of liquid fromthe nozzle onto a workpiece.

2. The nozzle of claim 1 wherein said passage is in substantiallytangential alignment with said vortex generating surface.

3. The nozzle of claim 2 wherein said passage is oriented in a planenormal to the axis of the nozzle.

4. The nozzle of claim 3 wherein said vortex generating surface slopesat an acute angle to the axis of the nozzle toward the outlet.

5. A coolant discharging nozzle comprising an annular body having aliquid inlet port, an annular nozzle insert removably connected to saidbody, the interior surface of said body and the exterior surface of saidinsert defining the boundaries of a plenum chamber communicating withsaid inlet port, said insert having a vortex generating surface and atleast one passage communicating with said plenum chamber and insubstantially tangential alignment with said vortex generating surface,said insert also having a contoured surface continuous with said vortexgenerating surface, said contoured surface having a portion which tapersaway from the axis of the nozzle to form the boundary of a hollowfrustrum having its base at the outlet of the nozzle for shaping anddirecting a swirling annular sheet of liquid from the nozzle onto aworkpiece.

1. A coolant discharging nozzle comprising an annular body having aliquid inlet port, an annular plenum chamber communicating with saidport, a vortex generating surface adapted to receive a liquid flowingfrom said plenum chamber through at least one passage between the plenumchamber and the interior of the nozzle and a contoured surfacecontinuous with said vortex generaating surface, said contoured surfacehaving a portion which tapers away from the axis of the nozzle to formthe boundary of a hollow frustrum having its base at the outlet of thenozzle for shaping and directing a swirling annular sheet of liquid fromthe nozzle onto a workpiece.
 2. The nozzle of claim 1 wherein saidpassage is in substantially tangential alignment with said vortexgenerating surface.
 3. The nozzle of claim 2 wherein said passage isoriented in a plane normal to the axis of the nozzle.
 4. The nozzle ofclaim 3 wherein said vortex generating surface slopes at an acute angleto the axis of the nozzle toward the outlet.
 5. A coolant dischargingnozzle comprising an annular body having a liquid inlet port, an annularnozzle insert removably connected to said body, the interior surface ofsaid body and the exterior surface of said insert defining theboundaries of a plenum chamber communicating with said inlet port, saidinsert having a vortex generating surface and at least one passagecommunicating with said plenum chamber and in substantially tangentialalignment with said vortex generating surface, said insert also having acontoured surface continuous with said vortex generating surface, saidcontoured surface having a portion which tapers away from the axis ofthe nozzle to form the boundary of a hollow frustrum having its base atthe outlet of the nozzle for shaping and directing a swirling annularsheet of liquid from the nozzle onto a workpiece.